PROJECT SUMMARY/ABSTRACT The purpose of this randomized controlled trial is to examine the impact of an antenatal milk expression (AME) intervention versus an attention control condition on breastfeeding outcomes among a sample of nulliparous, non-diabetic women with pre-pregnancy body mass indices ? 25. AME involves milk expression and collection in the third pregnancy trimester and is theorized to address multiple barriers to breastfeeding among overweight and obese women, including impaired breastfeeding self-efficacy, insufficient milk supply (critical- period endocrine modulation of milk volume), and early formula supplementation in the context of a medically- complex birth (availability of banked antenatal milk). Although AME is increasing in popularity outside the U.S., there is a lack of evidence to support its widespread adoption among women both with and without risk factors for poor breastfeeding outcomes. In the proposed study, participants will be enrolled at 34-366/7 gestational weeks and allocated into one of two study arms: 1) AME instruction delivered by remote, live International Board Certified Lactation Consultants via an innovative app-based telelactation platform trialed in our previous research; or 2) an attention control condition (video-based infant care education unrelated to infant feeding). AME instruction or control group video education will occur in weekly study visits from 37 to 40 weeks gestation, with women in the intervention group continuing AME 1-2 times per day at home. Specific aims are to: 1) determine the effect of the AME intervention on short-term breastfeeding outcomes, including breastfeeding self-efficacy and exclusivity, to two weeks postpartum; 2) to explore the sustained effect of the AME intervention on longer-term breastfeeding duration and exclusivity over the first year postpartum; and 3) to examine participants? experiences with and perceptions of AME. Data for Aims 1 and 2 will be captured via medical record review and in-person and remote survey completion at enrollment and postpartum follow-ups at 2 weeks, 6 weeks, 12 weeks, 6 months, and 12 months postpartum. For Aim 3, maternal perceptions about and experiences with AME will be captured via in-depth interviews at 6 weeks postpartum. Using an intention- to-treat approach, generalized linear mixed-effects modeling and Cox proportional hazards regression will be used to examine the effect of treatment assignment (AME vs. control) on quantitative outcomes. Sensitivity analyses will be conducted to determine receipt and ?dose? of AME on outcomes. We will also explore the role of maternal perception of milk supply and onset of lactogenesis II (copious milk production in the days following birth) in post-hoc mediational analyses. This project leverages our study team?s ongoing research investigating feasibility and preliminary efficacy of AME among normal weight and overweight/obese first-time mothers and feasibility of telelactation-delivered breastfeeding support. Results will inform clinical practice and policy regarding evidence-based breastfeeding support for overweight and obese women.